Antimicrobial activity of leucine‐substituted decoralin analogs with lower hemolytic activity

Linear cationic α‐helical antimicrobial peptides are promising chemotherapeutics. Most of them act by different mechanisms, making it difficult to microorganisms acquiring resistance. Decoralin is an example of antimicrobial peptide; it was described by Konno et al. and presented activity against microorganisms, but with pronounced hemolytic activity. We synthesized leucine‐substituted decoralin analogs designed based on important physicochemical properties, which depend on the maintenance of the amphiphilic α‐helical tendency of the native molecule. Peptides were synthesized, purified, and characterized, and the conformational studies were performed. The results indicated that the analogs presented both higher therapeutic indexes, but with antagonistic behavior. While [Leu]¹⁰‐Dec‐NH₂ analog showed similar activity against different microorganisms (c.a. 0.4–0.8 μmol L^?1), helical structuration, and some hemolytic activity, [Leu]⁸‐Dec‐NH₂ analog did not tend to helical structure and presented antimicrobial activities two orders higher than the other two peptides analyzed. On the other hand, this analog showed to be the less hemolytic (MHC value = 50.0 μmol L^?1). This approach provided insight for understanding the effects of the leucine substitution in the amphiphilic balance. They led to changes on the conformational tendency, which showed to be important for the mechanism of action and affecting antimicrobial and hemolytic activities. Copyright © 2017 European Peptide Society and John Wiley & Sons, Ltd.     

Design,synthesis and biological activity of cell‐penetrating peptide‐modified octreotide analogs

Four novel octreotide analogs with cell‐penetrating peptides (CPPs) at the N‐terminus or C‐terminus were synthesized by a stepwise Fmoc solid‐phase synthesis strategy. The synthesized peptides were analyzed and characterized using reverse phase HPLC and MALDI‐TOF mass spectrometry. The antiproliferative activity of the analogs was tested in vitro on human gastric (SGC‐7901) and hepatocellular cancer (BEL7402) cell lines using the 3‐(4,5‐dimethylthiazol‐2‐yl)‐2,5‐diphenyltetrazolium bromide (MTT) assay. Interestingly, these analogs showed a higher anticancer activities than the parent octreotide except CMTPT03 analog. The results demonstrate that the designed octreotide analogs enhance their anticancer activity after linking together the CPPs to octreotide at the N‐terminus, and are potential molecules for future use in cancer therapy and drug targeting. Copyright © 2009 European Peptide Society and John Wiley & Sons, Ltd.     

Antimicrobial activity,bactericidal mechanism and LPS‐neutralizing activity of the cell‐penetrating peptide pVEC and its analogs

pVEC is a cell‐penetrating peptide derived from the murine vascular endothelial‐cadherin protein. To evaluate the potential of pVEC as antimicrobial peptide (AMP), we synthesized pVEC and its analogs with Trp and Arg/Lys substitution, and their antimicrobial and lipopolysaccharide (LPS)‐neutralizing activities were investigated. pVEC and its analogs displayed a potent antimicrobial activity (minimal inhibitory concentration: 4–16 μM) against Gram‐positive and Gram‐negative bacteria but no or less hemolytic activity (less than 10% hemolysis) even at a concentration of 200 μM. These peptides induced a near‐complete membrane depolarization (more than 80%) at 4 μM against Staphylococcus aureus and a significant dye leakage (35–70%) from bacterial membrane‐mimicking liposome at a concentration as low as 1 μM. The fluorescence profiles of pVEC and its analogs in dye leakage from liposome and membrane depolarization were similar to those of a frog‐derived AMP, magainin 2. These results suggest that pVEC and its analogs kill bacteria by forming a pore or ion channel in the cytoplasmic membrane. pVEC and its analogs significantly inhibited nitric oxide production or tumor necrosis factor‐α release in LPS‐stimulated mouse macrophage RAW264.7 cells at 10 to 50 μM, in which RAW264.7 were not damaged. Taken together, our results suggest that pVEC and its analogs with potent antimicrobial and LPS‐neutralizing activities can serve as AMPs for the treatment of microbial infection and sepsis. Copyright © 2011 European Peptide Society and John Wiley & Sons, Ltd.     

Structure‐activity relationship studies of shortened analogues of the antimicrobial peptide EeCentrocin 1 from the sea urchin Echinus esculentus

EeCentrocin 1 is a potent antimicrobial peptide isolated from the marine sea urchin Echinus esculentus. The peptide has a hetero‐dimeric structure with the antimicrobial activity confined in its largest monomer, the heavy chain (HC), encompassing 30 amino acid residues. The aim of the present study was to develop a shorter drug lead peptide using the heavy chain of EeCentrocin 1 as a starting scaffold and to perform a structure‐activity relationship study with sequence modifications to optimize antimicrobial activity. The experiments consisted of 1) truncation of the heavy chain, 2) replacement of amino acids unfavourable for in vitro antimicrobial activity, and 3) an alanine scan experiment on the truncated and modified heavy chain sequence to identify essential residues for antimicrobial activity. The heavy chain of EeCentrocin 1 was truncated to less than half its initial size, retaining most of its original antimicrobial activity. The truncated and optimized lead peptide ( P6 ) consisted of the 12 N‐terminal amino acid residues from the original EeCentrocin 1 HC sequence and was modified by two amino acid replacements and a C‐terminal amidation. Results from the alanine scan indicated that the generated lead peptide ( P6 ) contained the optimal sequence for antibacterial activity, in which none of the alanine scan peptides could surpass its antimicrobial activity. The lead peptide ( P6 ) was also superior in antifungal activity compared to the other peptides prepared and showed minimal inhibitory concentrations (MICs) in the low micromolar range. In addition, the lead peptide ( P6 ) displayed minor haemolytic and no cytotoxic activity, making it a promising lead for further antimicrobial drug development.     

Effective antimicrobial activity of Cbf‐K16 and Cbf‐A7A13 against NDM‐1‐carrying Escherichia coli by DNA binding after penetrating the cytoplasmic membrane in vitro

New Delhi metallo‐beta‐lactamase‐1(NDM‐1)‐carrying isolates, which are resistant to most clinical used antibiotics except for tigecycline and colistin, have been found worldwide. Cathelicidin‐BF (BF‐30) is found in the venom of the snake Bungarus fasciatus and exhibits broad antimicrobial activity. Cbf‐K₁₆ and Cbf‐A₇A₁₃ were obtained by mutating Lys¹⁶, Ala⁷, and Ala¹³ of BF‐30, respectively. To investigate their antimicrobial activities against NDM‐1 carrying bacteria, recombinant Escherichia coli BL21 (DE3)‐NDM‐1 with high NDM‐1 activity was constructed by inserting the Klebsiella pneumoniae NDM‐1 gene (GenBank accession no. HQ328085) into a pET28a vector and transforming it into E. coli BL21 (DE3). The peptides showed effective antimicrobial activities against NDM‐1‐carrying E. coli, and the minimum inhibitory concentrations of Cbf‐K₁₆ and Cbf‐A₇A₁₃ were only 4 and 8 µg/ml, whereas those of minimum bactericidal concentrations were 8 and 16 µg/ml, respectively. A time course experiment showed that colony forming unit counts rapidly decreased, and bacteria were thoroughly eliminated within 3 and 6 h by the Cbf‐K₁₆ and Cbf‐A₇A₁₃ treatments, respectively. The peptides penetrated the bacterial cell membrane and enabled β‐galactosidase leakage, and caused the cytoplasmic membrane to become permeable, and finally bound to the DNA. The genomic DNA of E. coli was completely unable to migrate on an agarose gel after Cbf‐K₁₆ treatment (8 µg/ml). These data demonstrated that Cbf‐K₁₆ and Cbf‐A₇A₁₃ possess effective antimicrobial activity against drug‐resistant strains, including NDM‐1 carrying E. coli BL21 (DE3)‐NDM‐1, by binding to DNA after penetrating the cytoplasmic membrane in vitro, which may have potential therapeutic value for the treatment of NDM‐1‐carrying bacterial infections. Copyright © 2013 European Peptide Society and John Wiley & Sons, Ltd.     

The chitin‐binding capability of Cy‐AMP1 from cycad is essential to antifungal activity

Antimicrobial peptides are important components of the host innate immune responses by exerting broad‐spectrum microbicidal activity against pathogenic microbes. Cy‐AMP1 found in the cycad (Cycas revoluta) seeds has chitin‐binding ability, and the chitin‐binding domain was conserved in knottin‐type and hevein‐type antimicrobial peptides. The recombinant Cy‐AMP1 was expressed in Escherichia coli and purified to study the role of chitin‐binding domain. The mutants of Cy‐AMP1 lost chitin‐binding ability completely, and its antifungal activity was markedly decreased in comparison with native Cy‐AMP1. However, the antimicrobial activities of the mutant peptides are nearly identical to that of native one. It was suggested that the chitin‐binding domain plays an essential role in antifungal, but not antimicrobial, activity of Cy‐AMP1. Copyright © 2009 European Peptide Society and John Wiley & Sons, Ltd.     

Synthesis,biological activity and solution structure of new analogues of the antimicrobial Gramicidin S

Gramicidin S (GS) is a cyclo‐decapeptide antibiotic isolated from Bacillus brevis. The structural studies have shown that GS forms a two‐stranded antiparallel β‐sheet imposed by two II′ β‐turns. Despite its wide Gram+ and Gram? antimicrobial spectrum, GS is useless in therapy because of its high hemotoxicity in humans. It was found, however, that the analogues of GS‐14 (GS with 14 amino acid residues) attained a better antimicrobial selectivity when their amphipatic moments were perturbed. In this study, we report effects of similar perturbations imposed on GS cyclo‐decapeptide analogues. Having solved their structures by NMR/molecular dynamics and having tested their activities/selectivities, we have concluded that the idea of perturbation of the amphipatic moment does not work for GS‐10_0 analogues. An innovative approach to the synthesis of head‐to‐tail cyclopeptides was used. Copyright © 2010 European Peptide Society and John Wiley & Sons, Ltd.     

Structure‐activity relationship of indolicidin,a Trp‐rich antibacterial peptide

A series of Trp and Arg analogs of antibacterial indolicidin (Ind) was synthesized and the antimicrobial and hemolytic activities were investigated. [L⁹]Ind, [L¹¹]Ind, [K⁸,L⁹]Ind and [K^{6, 8},L⁹]Ind showed desirable characteristics, exhibiting negligible hemolytic activity while keeping strong antibacterial activity. The results indicated that the Trp residue at position 11 essentially contributes to both activities and one can not be exchanged for the other, whereas the Trp residues at positions 4 and 9 play important roles in antimicrobial and hemolytic activities, respectively. The Trp residues at positions 6 and 8 play no important roles in biological activities. We then found that the retro analog of Ind showed higher antibacterial activity than Ind against both Gram‐positive and Gram‐negative bacteria but remarkably lower hemolytic activity than that of Ind. Copyright © 2010 European Peptide Society and John Wiley & Sons, Ltd.     

Enantiomeric 9‐mer peptide analogs of protaetiamycine with bacterial cell selectivities and anti‐inflammatory activities

Protaetiamycine is an insect defensin, derived from the larvae of the beetle Protaetia brevitarsis. In our previous work, we designed 9‐mer peptide analogs of protaetiamycine, including 9Pbw2 (RLWLAIKRR‐NH₂), 9Pbw3 (RLWLAIWRR‐NH₂), and 9Pbw4 (RLWLAWKRR‐NH₂). 9Pbw2 and 9Pbw4 showed high antimicrobial activity without cytotoxicity, while 9Pbw3 with higher hydrophobicity compared to 9Pbw2 and 9Pbw4 showed high cytotoxicity as well as high antimicrobial activity (Shin et al., J. Pept. Sci. 2009; 15: 559–568). In this study, we investigated the anti‐inflammatory activities of 9Pbw2, 9Pbw3, and 9Pbw4 by quantitation of NO production in LPS‐stimulated RAW264.7 cells. The results showed that only 9Pbw3 has strong inhibition of NO production, implying that Trp⁷ as well as optimum level of hydrophobicity may play key roles in the anti‐inflammatory activity of 9Pbw3. In order to design potent anti‐inflammatory peptide with lower cytotoxicity as well as high stability from cleavage by protease compared to 9Pbw3, we synthesized 9Pbw3‐D , the all‐D ‐amino acid analog of 9Pbw3. 9Pbw3‐D showed less cytotoxicity against RAW264.7 cells as well as considerably stronger inhibition of NO production and inflammation‐induced cytokine production in LPS‐stimulated RAW264.7 cells than 9Pbw3. 9Pbw3‐D inhibited the gene expression of inflammatory‐induced cytokine significantly more than 9Pbw3 and showed high resistance to proteolytic digestion. Binding of 9Pbw3‐D with LPS caused higher enhancement of the FITC fluorescence as a result of its stronger interaction with LPS compared to that of 9Pbw3 and this result is in good agreement with their anti‐inflammatory activities. 9Pbw3‐D with higher anti‐inflammatory activity as well as lower cytotoxicity against mammalian cell compared to 9Pbw3 can be a potent noncytotoxic antibiotic candidates. Copyright © 2011 European Peptide Society and John Wiley & Sons, Ltd.     

Structure‐activity relationship of Trp‐containing analogs of the antimicrobial peptide gomesin

Gomesin (Gm) has a broad antimicrobial activity making it of great interest for development of drugs. In this study, we analyzed three Gm analogs, [Trp¹]‐Gm, [Trp⁷]‐Gm, and [Trp⁹]‐Gm, in an attempt to gain insight into the contributions of different regions of the peptide sequence to its activity. The incorporation of the tryptophan residue in different positions has no effect on the antimicrobial and hemolytic activities of the Gm analogs in relation to Gm. Spectroscopic studies (circular dichroism, fluorescence and absorbance) of Gm and its analogs were performed in the presence of SDS, below and above its critical micelle concentration (CMC) (~8 mM), in order to monitor structural changes induced by the interaction with this anionic surfactant (0–15 mM). Interestingly, we found that the analogs interact more strongly with SDS at low concentrations (0.3‐6.0 mM) than close to or above its CMC. This suggests that SDS monomers are able to cover the whole peptide, forming large detergent‐peptide aggregates. On the other hand, the peptides interact differently with SDS micelles, inserting partially into the micelle core. Among the peptides, Trp in position 1 becomes more motionally‐restricted in the presence of SDS, probably because this residue is located at the N‐terminal region, which presents higher conformational freedom to interact stronger with SDS molecules. Trp residues in positions 7 and 9, close to and in the region of the turn of the molecule, respectively, induced a more constrained structure and the compounds cannot insert deeper into the micelle core or be completely buried by SDS monomers. Copyright © 2014 European Peptide Society and John Wiley & Sons, Ltd.     

Enhancement of the anti‐inflammatory activity of temporin‐1Tl‐derived antimicrobial peptides by tryptophan,arginine and lysine substitutions

Temporin‐1Tl (TL) is a 13‐residue frog antimicrobial peptide (AMP) exhibiting potent antimicrobial and anti‐inflammatory activity. To develop novel AMP with improved anti‐inflammatory activity and antimicrobial selectivity, we designed and synthesized a series of TL analogs by substituting Trp, Arg and Lys at selected positions. Except for Escherichia coli and Staphylococcus epidermidis, all TL analogs exhibited retained or increased antimicrobial activity against seven bacterial strains including three methicillin‐resistant Staphylococcus aureus strains compared with TL. TL‐1 and TL‐4 showed a little increase in antimicrobial selectivity, while TL‐2 and TL‐3 displayed slightly decreased antimicrobial selectivity because of their about twofold increased hemolytic activity. All TL analogs demonstrated greatly increased anti‐inflammatory activity, evident by their higher inhibition of the production tumor necrosis factor‐α (TNF‐α) and nitric oxide and the mRNA expression of inducible nitric oxide synthase and TNF‐α in lipopolysaccharide (LPS)‐stimulated RAW264.7 macrophage cells, compared with TL. Taken together, the peptide anti‐inflammatory activity is as follows: TL‐2 ≈ TL‐3 ≈ TL‐4 > TL‐1 > TL. In addition, LPS binding ability of the peptides corresponded with their anti‐inflammatory activity. These results apparently suggest that the anti‐inflammatory activity of TL analogs is associated with the direct binding ability between these peptides and LPS. Collectively, our designed TL analogs possess improved anti‐inflammatory activity and retain antimicrobial activity without a significant increase in hemolysis. Therefore, it is evident that our TL analogs constitute promising candidates for the development of peptide therapeutics for gram‐negative bacterial infection. Copyright © 2015 European Peptide Society and John Wiley & Sons, Ltd.     

Immobilization and orientation‐dependent activity of a naturally occurring antimicrobial peptide

A naturally occurring antimicrobial peptide, SMAP‐29, was synthesized with an n‐terminal or c‐terminal cysteine, termed c_SMAP and SMAP_c, respectively, for site‐directed immobilization to superparamagnetic beads. Immobilized SMAP orientation‐dependent activity was probed against multiple bacteria of clinical interest including Acinetobacter baumannii, Pseudomonas aeruginosa, Bacillus anthracis sterne and Staphylococcus aureus. A kinetic microplate assay was employed to reveal both concentration and time‐dependent activity for elucidation of minimum bactericidal concentration (MBC) and sub‐lethal effects. Immobilized SMAP activity was equivalent or reduced compared with soluble SMAP_c and c_SMAP regardless of immobilization orientation, with only one exception. A comparison of immobilized SMAP_c and c_SMAP activity revealed a bacteria‐specific potency dependent on immobilization orientation, which was contrary to that seen in solution, wherein SMAP_c was more potent against all bacteria than c_SMAP. Sub‐MBC kinetic studies displayed the influence of peptide exposure to the cells with multiple bacteria exhibiting increased susceptibility and efficacy at lower concentrations upon extended exposure (i.e. MBC enhancement). For instances in which complete killing was not achieved, two predominant effects were evident: retardation of growth rate and an increased lag phase. Both effects, seen independently and concomitantly, indicate some degree of induced cellular damage that can serve as a predictor toward eventual cell death. SMAP_c immobilized on glass through standard silanization chemistry was also investigated to ascertain the influence of substrate on activity against select bacteria. Published 2015. This article is a U.S. Government work and is in the public domain in the USA.     

Antimicrobial activity of human α‐defensin 6 analogs: insights into the physico‐chemical reasons behind weak bactericidal activity of HD6 in vitro

Human α‐defensin 6 (HD6), unlike other mammalian defensins, does not exhibit bactericidal activity, particularly against aerobic bacteria. Monomeric HD6 has a tertiary structure similar to other α‐defensins in the crystalline state. However, the physico‐chemical reasons behind the lack of antibacterial activity of HD6 are yet to be established unequivocally. In this study, we have investigated the antimicrobial activity of HD6 analogs. A linear analog of HD6, in which the distribution of arginine residues was similar to active α‐defensins, shows broad‐spectrum antimicrobial activity, indicating that atypical distribution of arginine residues contributes to the inactivity of HD6. Peptides spanning the N‐terminal cationic segment were active against a wide range of organisms. Antimicrobial potency of these shorter analogs was further enhanced when myristic acid was conjugated at the N‐terminus. Cytoplasmic localization of the analogs without fatty acylation was observed to be necessary for bacterial killing, while they exhibited fungicidal activity by permeabilizing Candida albicans membranes. Myristoylated analogs and the linear full‐length arginine analog exhibited activity by permeabilizing bacterial and fungal membranes. Our study provides insights into the lack of bactericidal activity of HD6 against aerobic bacteria. Copyright © 2015 European Peptide Society and John Wiley & Sons, Ltd.     

Antimicrobial peptide PMAP‐37 analogs: Increasing the positive charge to enhance the antibacterial activity of PMAP‐37

Bacterial resistance induced by the use of antibiotics has provided a chance for the development of antimicrobial peptides (AMPs), and modification of AMPs to enhance the antibacterial activity or stability has become a research focus. PMAP‐37 is an AMP isolated from porcine myeloid marrow, and studies on its modification have not yet been reported. In this study, three PMAP‐37 analogs named PMAP‐37(F9‐R), PMAP‐37(F34‐R), and PMAP‐37(F9/34‐R) were designed by residue substitution to enhance the positive charge. The antimicrobial activity of PMAP‐37 and its analogs in vitro and in vivo were detected. The results showed that compared with PMAP‐37, PMAP‐37(F9‐R) and PMAP‐37(F9/34‐R) exhibited antibacterial activity against S. flexneri CICC21534. Although PMAP‐37(F34‐R) had no antibacterial activity against S. flexneri CICC21534, its minimal inhibitory concentrations (MICs) were significantly lower than those of PMAP‐37 against most bacterial strains. Besides, all PMAP‐37 analogs were pH stable, retaining stable antibacterial activity after treatment with solution from pH 2 to pH 8/9. In addition, the PMAP‐37 analogs displayed increased thermal stability, and PMAP‐37(F34‐R) retained >60% antibacterial activity after boiling for 2 hours. Furthermore, the PMAP‐37 analogs exhibited impressive therapeutic efficacy in bacterial infections by reducing bacterial burden and inflammatory damage in the lung and liver, resulting in a reduction in mortality. Notably, the therapeutic effect of PMAP‐37(F34‐R) was comparable to that of ceftiofur sodium, and even superior to antibiotics in L. monocytogenes CICC21533 infection model. In conclusion, the PMAP‐37(F34‐R) may be a candidate for the treatment of bacterial infections in the clinic.     

Design,expression, and characterization of the hybrid antimicrobial peptide T‐catesbeianin‐1 based on FyuA

The overuse of antibiotics has resulted in the emergence of antibiotic‐resistant bacteria, which presents an urgent need for new antimicrobial agents. At present, antimicrobial peptides have attracted a great deal of attention from researchers. However, antimicrobial peptides often affect a broad range of microorganisms, including the normal flora in a host organism. In the present study, we designed a novel hybrid antimicrobial peptide, expressed the hybrid peptide, and studied its specific target. The hybrid peptide, named T‐catesbeianin‐1, which includes the FyuA‐binding domain of pesticin and the peptide catesbeianin‐1, was designed and expressed in Pichia pastoris X‐33. Then, we determined the antimicrobial activity, cytotoxicity, and specific target of the peptide. T‐catesbeianin‐1 has strong antimicrobial activity and binds to FyuA to inhibit or kill Escherichia coli present in clinical specimens and mixed‐species culture. In summary, these findings suggested that T‐catesbeianin‐1 might be promising and specific antibiotic agent for therapeutic application against fyuA⁺ E. coli.     

Antibiotic activity and structural analysis of the scorpion-derived antimicrobial peptide IsCT and its analogs

IsCT is a non-cell-selective antimicrobial peptide isolated from the scorpion Opisthacanthus madagascariensis that has potent cytolytic activity against both mammalian and bacterial cells. To investigate the structure-activity relationships of IsCT and to design novel peptide antibiotics with bacterial cell selectivity, we synthesized several analogs of IsCT and determined their three-dimensional structures in solution by 2D-NMR spectroscopy. IsCT has a linear alpha-helical structure from Gly3 to Phe13, and [K7]-IsCT has a linear alpha-helical structure from Leu2 to Phe13. [K7, P8, K11]-IsCT, which has a bend in its middle region, exhibited the highest antibacterial activity without hemolytic activity, suggesting that its proline-induced bend is an important determinant of this selectivity. Tryptophan fluorescence showed that the high selectivity of [K7, P8, K11]-IsCT toward bacterial cells is closely correlated with its highly selective interaction with negatively charged phospholipids. Its potent activity against antibiotic-resistant bacteria suggests that [K7, P8, K11]-IsCT may serve as a promising lead candidate in the development of new peptide antibiotics.     

Synthesis and biological activity of lipophilic analogs of the cationic antimicrobial active peptide anoplin

Anoplin is a short natural cationic antimicrobial peptide which is derived from the venom sac of the solitary wasp, Anoplius samariensis. Due to its short sequence G¹LLKR⁵IKT⁸LL‐NH₂, it is ideal for research tests. In this study, novel analogs of anoplin were prepared and examined for their antimicrobial, hemolytic activity, and proteolytic stability. Specific substitutions were introduced in amino acids Gly¹, Arg⁵, and Thr⁸ and lipophilic groups with different lengths in the N‐terminus in order to investigate how these modifications affect their antimicrobial activity. These cationic analogs exhibited higher antimicrobial activity than the native peptide; they are also nontoxic at their minimum inhibitory concentration (MIC) values and resistant to enzymatic degradation. The substituted peptide GLLKF⁵IKK⁸LL‐NH₂ exhibited high activity against Gram‐negative bacterium Zymomonas mobilis (MIC = 7 µg/ml), and the insertion of octanoic, decanoic, and dodecanoic acid residues in its N‐terminus increased the antimicrobial activity against Gram‐positive and Gram‐negative bacteria (MIC = 5 µg/ml). The conformational characteristics of the peptide analogs were studied by circular dichroism. Structure activity studies revealed that the substitution of specific amino acids and the incorporation of lipophilic groups enhanced the amphipathic α‐helical conformation inducing better antimicrobial effects. Copyright © 2016 European Peptide Society and John Wiley & Sons, Ltd.     

Ghrelin—a novel generation of anti‐obesity drug: design,pharmacomodulation and biological activity of ghrelin analogues

Ghrelin is a unique bioactive peptide with respect to both the structure and its biological function. This 28‐amino acid peptide is modified with an n‐octanoyl group at serine‐3, and accordingly is the only lipidated biologically active peptide hormone known so far. Ghrelin binds to the so‐called ghrelin or GHS receptor, a member of the class A of G‐protein coupled receptors, which leads to Ca²⁺ release intracellularly due to the activation of the Gq‐system. Interestingly, the ghrelin receptor shows a significant constitutive activity which means that in addition to agonists and antagonists, inverse agonists play an important role in receptor modulation. In this review, the major activities of ghrelin are summarized with a strong focus on the regulation of food intake. So far reported agonists, antagonists and inverse agonists are shown and structure activitiy relationships are discussed. Furthermore, the application of ghrelin ligands as novel anti‐obesity drugs is outlined and the state of the art in this field is summarized. Copyright © 2009 European Peptide Society and John Wiley & Sons, Ltd.     

Peptide dendrimers as antifungal agents and carriers for potential antifungal agent—N3‐(4‐methoxyfumaroyl)‐(S)‐2,3‐diaminopropanoic acid—synthesis and antimicrobial activity

A series of peptide dendrimers and their conjugates with antimicrobial agent FMDP (N³‐(4‐methoxyfumaroyl)‐(S)‐2,3‐diamino‐propanoic acid) were synthesized. The obtained compounds were tested for the antibacterial and antifungal activity. All novel dendrimers displayed much better activity against the tested strains than FMDP itself. Moreover, their conjugates with FMDP also exhibited antimicrobial activity. The most promising molecules were tested against a broad selection of fungal strains. The analysis of their antifungal properties indicates that the examined molecules are efficient growth inhibitors of fluconazole‐resistant hospital‐acquired strains. Moreover, an application of amphiphilic branched peptides such as FMDP carriers suggests that transport mechanism involves more likely the cell membrane perturbation than the mediation of the specific transport proteins. The activity of obtained compounds strongly depends on the specific structure of the molecule.     

Short KR‐12 analogs designed from human cathelicidin LL‐37 possessing both antimicrobial and antiendotoxic activities without mammalian cell toxicity

KR‐12 (residues 18–29 of LL‐37) was known to be the smallest peptide of human cathelicidin LL‐37 possessing antimicrobial activity. In order to optimize α‐helical short antimicrobial peptides having both antimicrobial and antiendotoxic activities without mammalian cell toxicity, we designed and synthesized a series of KR‐12 analogs. Highest hydrophobic analogs KR‐12‐a5 and KR‐12‐a6 displayed greater inhibition of lipopolysaccharide (LPS)‐stimulated tumor necrosis factor‐α production and higher LPS‐binding activity. We have observed that antimicrobial activity is independent of charge, but LPS neutralization requires a balance of hydrophobicity and net positive charge. Among KR‐12 analogs, KR‐12‐a2, KR‐12‐a3 and KR‐12‐a4 showed much higher cell specificity for bacteria over erythrocytes and retained antiendotoxic activity, relative to parental LL‐37. KR‐12‐a5 displayed the strongest antiendotoxic activity but almost similar cell specificity as compared with LL‐37. Also, these KR‐12 analogs (KR‐12‐a2, KR‐12‐a3, KR‐12‐a4 and KR‐12‐a5) exhibited potent antimicrobial activity (minimal inhibitory concentration: 4 μM) against methicillin‐resistant Staphylococcus aureus. Taken together, these KR‐12 analogs have the potential for future development as a novel class of antimicrobial and anti‐inflammatory therapeutic agents. Copyright © 2013 European Peptide Society and John Wiley & Sons, Ltd.